The utility model provides a be used for pneumatic fixture device of transmission shaft support welded, including base and two clamping mechanism s of setting at the base opposite side, the base includes two support posts and sets up the workstation on two support post tops, and both sides that the workstation up end corresponds clamping mechanism are provided with the spacer pin respectively, clamping mechanism includes cylinder, connecting rod, branch and pressure head, and the cylinder setting is in one side of workstation, and branch sets up between cylinder and workstation, and the middle part of connecting rod is articulated with the branch top, the one end of connecting rod and the piston rod hinge of cylinder, the pressure head sets up the other end at the connecting rod. The utility model discloses only need one -man operation, practiced thrift the cost of labor, moreover owing to self -holding for the welding quality of support is very stable, and welding precision is high, thereby can guarantee to produce the spare part of high accuracy.